For machining workpieces of complex shape, which for their production must pass through a relatively large number of different metal-cutting machining processes, especially for mass-scale machining or production of such workpieces, machine tools are often used that on the same workpiece successively perform different machining operations from different directions. One example of such a machine tool can be found in U.S. Pat. No. 5,452,502. The machine tool disclosed there is embodied as a circular indexing machine tool and has a cross-shaped workpiece carrier disposed inside a cage-like base frame. Workpiece receptacle devices are disposed on the side faces of the arms of the cross-shaped workpiece carrier. While the workpiece carrier can be rotated and indexed about a vertical axis, the individual workpiece receptacles are each rotatable about horizontal axes, which are disposed at a tangent to an imaginary circle. As the workpiece carriers index onward, the workpieces successively pass through different work stations. These stations are defined by machining units, which are retained on the basic frame so as to be adjustable in multiple directions. Each machining unit has one work spindle, which is provided with a revolver head. The revolver head is embodied as a crown type turret head. Its spindles are driven jointly by the work spindle. By revolution of the revolver head, a desired tool can be transferred into a rectilinear lengthening position of the work spindle, thus putting it in the machining position. All the spindles of the revolver head are driven simultaneously, and they continue to move even during the rotation or onward indexing of the revolver head.
With this circular increment machine tool, five-sided machining of the workpieces is possible, which makes for high efficiency. However, oblique faces or oblique bores, that is, bores that do not form a right angle with the axis of rotation (horizontal axis) of the workpiece, present a certain problem in machining. In special cases, in which because of the workpiece design different machining times are needed in the various work stations, it is also possible that the machining units of different work stations may work for variously long times. The indexing time is determined by the longest machining time required.